There are a couple limitations to all of the special textures we have seen (from textures, pigment and normal maps
through material maps). First, if we have used the default directive to set the default texture for all items in our
scene, it will not accept any of the special textures discussed here. This is really quite minor, since we can always
declare such a texture and apply it individually to all objects. It does not actually prevent us from doing anything
we could not otherwise do.

The other is more limiting, but as we will shortly see, can be worked around quite easily. If we have worked with
layered textures, we have already seen how we can pile multiple texture patterns on top of one another (as long as one
texture has transparency in it). This very useful technique has a problem incorporating the special textures we have
just seen as a layer. But there is an answer!

For example, say we have a layered texture called Speckled_Metal, which produces a silver metallic
surface, and then puts tiny specks of rust all over it. Then we decide, for a really rusty look, we want to create
patches of concentrated rust, randomly over the surface. The obvious approach is to create a special texture pattern,
with transparency to use as the top layer. But of course, as we have seen, we would not be able to use that texture
pattern as a layer. We would just generate an error message. The solution is to turn the problem inside out, and make
our layered texture part of the texture pattern instead, like this

And the ultimate effect is the same as if we had layered the rust patches on to the speckled metal anyway.

With the full array of patterns, pigments, normals, finishes, layered and special textures, there is now
practically nothing we cannot create in the way of amazing textures. An almost infinite number of new possibilities
are just waiting to be created!